This invention relates to fuel quantity measurement. It is particulary useful for fuel quantity measurement for aircraft. The invention combines fiber optics and ultrasonics.
An ultrasonic measuring system is difficult to implement due to the requirement for a hardwired interface to each sensor. The wiring presents a hazard within the tank and is difficult to implement, especially for a wing tank, if the sensors are mounted outside the tank.
Many points must be sensed even to achieve a very coarse accuracy. The multifiber optic interconnection at the tank interface becomes unmanageable and very unreliable.
The invention provides remotely located ultrasonic transducers and control electronics powered from a central location over fiber optic tubes or bundles and returning time domain surface reflections from the fuel height by similar fiber optic cables or bundles. The optical power is converted at the transducer with an array of photo detectors, and stored capacitately until a measurement is requested.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of an opto-acoustic fuel quantity gauging system in accordance with the present invention.
FIG. 2 is a schematic representation of an optical powering circuit for use in accordance with the present invention.
FIG. 3 is a schematic representation of a transmitter triggering and excitation circuit for an opto-acoustic fuel quantity gauging system in accordance with the present invention.
FIG. 4 is a schematic representation of a receiver circuit for use in an opto-acoustic fuel quantity gauging system in accordance with the present invention.
BRIEF SUMMARY OF INVENTION
An opto-acoustic fuel quantity gauging system including at least one tank; at least one ultrasonic energy source; at least one ultrasonic energy sensor; and a detector circuit. The ultrasonic energy source is connected to the tank and the ultrasonic energy sensor is connected to the tank. Each ultrasonic energy sensor is connected to the detector by a fiber optic cable. The use of the optic-acoustic system of the invention improves the safety of fuel quantity gauging by elimination of potential spark sources. The opto-acoustic system of the invention also provides improved accuracy in the measurement of fuel quantity.
DETAILED DESCRIPTION OF THE INVENTION
The invention uses fiber optics for interfacing to ultrasonic sensors as shown in FIG. 1. The sensor is mounted in a cavity in the lower part of the wing tank. The sensor is easily removed and replaced. The fiber cables are mounted inside the tank and interface through the cavity. The multiplexed control unit transmits a 1 ms pulse which charges the energy source, followed by a short 1 mhz burst (preferably about 10 pulses) to drive the ultrasonic transmitter. The ultrasonic receiver, powered by the energy source, detects the reflected acoustic signal some time later (fraction of a millisecond), and converts the signal to light for transmission through the fiber optic cable back to the multiplexer.
The power dissipated by the sensor electronics is approximately 200 mw peak for the sensor transmit and receives cycles of 10 microseconds. Duty cycle depends on the sensor sample time, or about once every 200 ms in duration.
Fuel level is sensed by transmitting an acoustic signal through the bottom of the tank to the surface of fuel and reflecting the signal back to a receiver. A time reference is measured over a known distance using a velocitometer. By calibrating against the time reference, the level is accurately determined. The fuel density is inferred by measuring the fuel temperature and speed of sound in the fuel determined from the time reference measurement.
An opto-acoustic system for fuel quantity gauging is shown in FIG. 1. The opto-acoustic fuel
quantity gauging system 10 includes a
tank 12 and a
detector circuit 14. The
tank 12 is provided with stillwell 20.
The opto-acoustic sensing and
transmission system 30 is connected to the
tank 12. The opto-
acoustic system 30 is connected by a fiber
optic cable 32 to the
optical detectors 34. The opto-
acoustic system 30 receives optical power through fiber
optic cable 36 from
optical power source 38.
Similarly, opto-acoustic sensing and
transmission system 40 is connected to
tank 12. Opto-
acoustic system 40 is adjacent to stillwell 41. Opto-
acoustic system 40 is connected by fiber
optic cable 42 to
optical detectors 34. Opto-
acoustic system 40 is connected by fiber
optic cable 46 to
optical power source 38. Opto-acoustic sensing and
transmission system 50 is connected to
tank 12. Discrete level detector opto-
acoustic system 50 is adjacent to a stillwell 51. Discrete level detector opto-
acoustic system 50 is connected by a fiber
optic cable 52 to
optical detectors 34. Discrete level detector opto-
acoustic system 50 is connected by fiber
optic cable 56 to
optical power source 38.
Reflector 57 is connected to stillwell 51 by
brackets 58.
Optical detectors 34 are connected by
electrical conductors 70, 71 and 72 to multiplexer 74.
Multiplexer 74 is connected to
signal conditioner 76 through
electrical conductor 78.
Multiplexer 74 is connected through
line 80 to central processing unit and
memory 82.
Signal conditioner 76 is connected through
line 84 to central processing unit and
memory 82. Central processing unit and
memory 82 is connected through
line 86 to
data interface 88.
Data interface 88 is connected through
line 90 to
indicator 92. Electrical current from
power supply 94 is received by
signal conditioner 76 through line 96.
Power supply 94 receives electrical current from the aircraft power supply 98 through
line 100.
With more particular reference to FIG. 2, the
power supply 94 is connected to
light bulb 104 by
line 106.
Light rays 107 from
bulb 104 pass through
lens 108 and into the bundled fiber ends 110.
Optical fiber 36 extends from bundled fiber ends 110 to
photo diodes 120.
Optical fiber 46 extends from bundled fiber ends 110 to
photo diodes 122.
Optical fiber 56 extends from bundled fiber ends 110 to
photo diode 123.
Photo diodes 120, 122 and 123 are connected in series to ground by
line 126. Capacitor 128 is connected to ground by
line 130.
Photo diodes 120, 122 and 123 are connected in parallel to
capacitor 128 by
lines 132 and 134.
FIG. 3 shows a preferred embodiment of a transmitter triggering and excitation circuit for the opto-
acoustic systems 30, 40 and 50. FIG. 4 shows a preferred embodiment of a receiver circuit for the opto-
acoustic systems 30, 40 and 50.
With more particular reference to FIG. 3, it would seem that the
photo diode 120 is connected to the optically driven
switch 140 by
line 142. Optically driven
switch 140 is connected to
SCR trigger 144 by
line 146.
SCR trigger 144 is connected to high
current switch 148 by
line 150. High
current switch 148 is connected to
ultrasonic transducer transmitter 152 by
line 154.
Ultrasonic transducer transmitter 152 is connected to
capacitor 156 by
line 158.
Conductor 160 is connected in parallel with
ultrasonic transducer transmitter 152 by
lines 162 and 164.
Capacitor 156 is connected through
line 166 to high
current switch 148.
Capacitor 156 is connected to line 168 to
resistor 170.
Resistor 170 is connected to
resistor 172 through
line 174.
Resistor 172 is connected to
SCR trigger 144 through
line 176.
Resistor 172 is connected to
capacitor 178 through
line 180.
Capacitor 178 is connected to ground through
line 182.
Resistor 170 and
resistor 172 are connected to the optically driven
switch 140 through
line 184. The optically driven
switch 140 is connected through
line 186 to
voltage reference 188 as shown in FIG. 4.
Voltage reference 188 is connected to the
amplifier limiter 190 through
line 192. The
ultrasonic transducer receiver 194 is connected to the
amplifier 190 through
lines 196 and 198. The inductor 200 is connected to
line 196 and
line 198. The voltage to
current converter 202 is connected to the
amplifier limiter 190 through
line 204. The voltage to
current converter 202 is connected to positive V through
line 108.
Amplifier limiter 190 is connected to positive V through
line 210. The infrared light emitting diode (LED) 212 is connected to voltage to
current converter 202 through
line 214. Light from
infrared LED 212 is transmitted through a fiber optic cable to
optical detectors 34.
Ultrasonic waves travel from the opto-
acoustic systems 30 and 40 within the stillwells 20 and 41 respectively to
fuel surface 250. The waves are reflected from the surface and then travel within the respective stillwells to the respective opto-acoustic system. Ultrasonic waves travel from discrete level detector opto-
acoustic system 50 along
stillwell 51 to
reflector 57. The waves are reflected from
reflector 57 and travel along the
stillwell 51 to the
system 50. When the fuel surface is above the
stillwell 51, the waves travel at a velocity associated with the fuel. As the fuel level passes through the
stillwell 51, the waves travel at a velocity associated with the fuel and air, until the fuel level is below the
stillwell 51. The velocity of the waves in the stillwell is characteristic of the level of fuel.
The
stillwells 20, 41 and 51 are preferably provided with
apertures 252. This improves the flow of fuel through the stillwell which improves the equilibration of the level of fuel between the
tank 12 and the stillwells.
In accordance with the present invention, optically delivered energy is stored in capacitors. A continuous optical power source drives an array of silicone detectors in series to provide capacitor charge voltage. Optical trigger switches are used on transmit burst and receiver signal processing. Signal processing amplifies and compresses the dynamic range of returned ultrasonic signals before modulating the return optical source.
Other features, advantages and specific embodiments of this invention will become readily apparent to those exercising ordinary skill in the art after reading the foregoing disclosures. In this regard, while specific embodiments of this invention have been described in considerable detail, variations and modifications of these embodiments can be effected without departing from the spirit and scope of the invention as disclosed and claimed.